Investigation of CuAlNi Shape Memory Alloy Doped with Graphene

Abstract

In the research area of shape memory alloys (SMAs), which are one of the most utilized class of smart materials, many additive alloying metal elements have been incorporated into shape memory alloy systems to improve or modify their functional and characteristic properties such as to get higher or lower martensitic transformation temperatures, to enhance shape recovery or superelasticity capabilities, to improve ductility or strength etc. Though the additive elements are often metals, some other materials can be added in SMA systems, too. Cu-based SMAs are regarded as the most potential alternative to the superior but expensive NiTi SMAs. Therefore, improving the SMA features of the Cu-based SMAs by some methods (such as doping additive elements into them, fabricating them by different production routes, etc.) have also become very attractive to the researchers who work in this area. In this experimental study, ternary CuAlNi shape memory alloy was doped by minor amount of pure graphene (in the form of nanoplatelets) via melting in vacuum arc melter under argon plasma. The alloy obtained in as-cast ingot form was cut into small pieces suited for a series of differential calorimetric and structural shape memory effect characterization measurements. Before conducting the tests, all of the alloy samples were solution-treated in high β–phase temperature region and instantaneously quenched in iced-brine water. By doing this fast cooling, the hypoeutectoid precipitations of α (Cu) and γ2 (Al) were surpassed and thus the β1’ martensite phase formed in the alloy texture, which phase constitutes the ground for a shape memory effect property to form in the alloys. Then, the alloys chemical composition was determined by EDX test result showing the presence of carbon content in the alloy. Thermal characterization tests were performed by DSC and DTA measurements taken at varying heating/cooling rates under inert argon athmosphere. The cyclic thermograms obtained by these thermal tests revealed the endothermic and exothermic martensitic transformation peaks occurred above 100 °C indicating the presence of shape memory effect property in the alloy. The structural X-ray diffraction test was carried out at room temperature at where the alloy was in martensite phase, expectedly the diffraction peaks formed by reftection of X-rays from the atomic planes of β1’ martensite structures were observed on the diffraction pattern of the alloy.